Time-related responses of spontaneously breathing, laterally recumbent horses to prolonged anesthesia with halothane.

The research article discusses the cardiovascular and respiratory responses of healthy adult horses during five hours of anesthesia with halothane, highlighting changes in arterial pressure, vascular resistance, cardiac output, and ventilation parameters.

Research Methodology

• The research included ten healthy, fasting, laterally recumbent adult horses which were breathing spontaneously.
• The horses were exposed to five hours of 1.06% alveolar halothane, 1.2 times the minimum alveolar concentration generally needed for horses.
• Cardiovascular and respiratory functions were quantitatively tracked and evaluated over time.

Key Findings

• The mean carotid arterial pressure in the horses became approximately 25% higher after one hour of halothane exposure. This peak was reached after 90 minutes, at which point it was about 30% higher than the initial 30-minute mark.
• Initially, total peripheral vascular resistance increased by roughly 20% at one hour, before gradually returning to its initial value over the next four hours.
• Cardiac output progressively increased over time due to an increase in stroke volume, increasing by approximately 20% by the second hour and by about 40% by the 5-hour mark.
• An increase in mixed venous PO2 paralleled the increase in cardiac output. However, heart rate remained largely unchanged.
• With regards to ventilation, some measures changed significantly over time. After four and five hours of halothane exposure, the partial pressure of carbon dioxide in arterial blood (PaCO2), inspired gas flow, and the ratio of inspired vs expired gas flow increased, compared to the initial half-hour values. After three hours, inspiratory time decreased significantly.

Conclusion

• All the horses involved in the study recovered from the anesthesia and recumbency without experiencing any complications.
• This study provides a detailed understanding of the physiological changes occurring in horses under prolonged halothane anesthesia, which is valuable in improving the handling and care of horses during and after procedures requiring extended anesthesia.